1. Field of Invention
The present invention relates to a filament lamp, and in particular, to a filament lamp used to heat an article to be treated.
2. Description of Related Art
Heat treatment devices capable of heating an article to be treated without making contact by optical irradiation from an incandescent lamp or other light source in which filaments are disposed inside a light-emitting tube composed of optically transparent material, for example, are widely used as heat treatment devices in rapid thermal processing (RPT) employed during the film formation, oxidation, impurity dispersion, nitriding, film stabilization, silicidation, crystallization, and ion implantation processes that are part of the semiconductor manufacturing process (see Japanese Unexamined Patent Application JP 7-37833 and Japanese Unexamined Patent Application JP 2002-203804).
One of the present inventors, with others, has proposed a filament lamp having the following configuration, using an optical irradiating type heat treatment device as a light source (see, commonly owned, Japanese Unexamined Patent Application JP 2006-279008 and corresponding U.S. Patent Application Publication 2006/0197454).
Describing this filament lamp in reference to FIG. 5, coil-shaped filaments 4, 5, and 6 are disposed in sequence extending in the tube axis direction of a light-emitting tube 1, within a straight-tube shaped light-emitting tube 1 wherein both ends are sealed airtight by end seals 2a and 2b. Both ends of the filaments 4, 5, and 6 have internal leads 4a, 4b, 5a, 5b, 6a, and 6b connected for supplying electric current.
The internal leads of each filament extend to the respective end seals and are electrically connected to external leads separately via metal foils. In other words, the internal leads 4a, 5a, and 6a on one end of each of the filaments 4, 5, and 6 are electrically connected to the external leads 10a, 11a, and 12a by metal foils 7a, 8a, and 9a on the end seals 2a. Similarly, the internal leads 4b, 5b, and 6b on the other end are electrically connected to the external leads 10b, 11b, and 12b by the metal foils 7b, 8b, and 9b on the end seal 2b. 
In addition, each of the filaments 4, 5, and 6 can be supplied with electric current separately by being connected to separate electric current supply devices 13, 14, and 15 by the external leads 10a, 10b, 11a, 11b, 12a, and 12b. 
Insulating tubes 16, 17, and 18 are fitted onto the internal leads 4b, 5a, 5b, 6a of the filaments 4, 5, 6, disposed at locations opposite the filaments 4, 5, 6.
In addition, circular anchors 19, 20, 21 are disposed alongside in the tube axis direction of the light-emitting tube 1 at locations between the inner wall of the light-emitting tube 1 and the insulating tubes 16, 17, 18. The filaments 4, 5, 6 are each supported by 2 anchors, for example, without making contact with the light-emitting tube 1.
Since electrical current can be supplied separately to a plurality of filaments and control performed separately for illumination, etc., of each filament using an optical irradiation type heat treatment device using filament lamps of this configuration, optical irradiation is possible with a preferred radiation intensity according to the properties of the article to be treated, even in a case, for instance, in which the distribution of the degree of localized temperature change on the article to be treated is asymmetrical with respect to the shape of the article to be treated. As a result, the article to be treated can be uniformly heated, and as a consequence, uniform temperature distribution can be realized across the entirety of the irradiated surface on the article to be treated, which confers a benefit.
In the conventional technology as described above, insulating tubes 16, 17, 18 are fitted in order to prevent electrical discharge between each filament 4, 5, 6 and the internal leads 4a, 5a, 5b, 6a. Accordingly, the light emitted from the filaments sometimes is blocked by the insulating tubes, causing the illumination distribution on the irradiated surface of the article to be treated to not be uniform, and thus, making it impossible to make the temperature distribution uniform, which is problematic.
Blockage of the emitted light from the central filament, disposed directly above the center of the article to be treated, exerts a highly adverse impact on the uniformity of temperature distribution on the article to be treated.
The foregoing description cited an example of fitting insulating tubes onto the internal leads, but even in a case in which no insulating tubes are present, the same problem of blockage of emitted light occurs.